1. Field of the Invention
This invention relates to a structural part of the type able to dissipate energy delivered during an impact compressing it along a defined axis, up to failure, especially in the event of a crash.
2. Description of the Related Art
A particularly preferred field of application of the invention is the field of aeronautics, in which the structural part can be advantageously utilized as a so-called crash part for an aircraft, i.e. a part taking part in locally dissipating energy delivered during a crash. However, the invention also applies to any other field in which it is advantageous to utilize a local energy dissipation system, in particular for crashes, notably but not exclusively in the field of Formula 1 vehicles.
In aeronautics, the invention's preferred application context, which will be described in a more specifically detailed, although in no way limiting, way in this description, ‘structural part’ means any part forming part of a structure, whether it is a so-called primary aircraft structure, i.e. one having to withstand significant mechanical loads, or a so-called secondary aircraft structure, i.e. one having to withstand low, or no, mechanical loads. Thus, the part according to the invention can be, or form part of, a fuselage frame of the aircraft, in particular of the airplane or helicopter, a spar, a cross-member, a sine-wave beam, referred to as a crash beam, i.e. where having a web which is corrugated so as to present increased resistance to buckling in one direction, etc.
In the aeronautics field, there is a growing need for the structural parts that are utilized, in particular parts made of composite material based on reinforcing fibers, to incorporate the function of locally dissipating energy in the event of a crash.
The systems or parts that currently exist for locally dissipating energy in the event of a crash generally comprise tubes, struts, sine-wave beams, boxes, etc. When they are applied to structures made of composite materials, these systems are designed to favor, in the event of a crash, as a result of a compressive force exerted in a predefined direction, a mode of failure by matting/fragmentation, favoring the progressive establishment of different types of intrinsic degradations of the composite plies (cracking) or interfaces (delamination), i.e. a mode of failure by local crushing in the direction of the force, rather than a mode of failure by buckling, i.e. by folding, or by violent failure, with misalignment of the pieces that slide alongside each other. The macroscopic matting/fragmentation failure mode notably has the advantage of generating little movement in the direction of the force applied on the part and of dissipating a much greater amount of energy than the modes of failure by buckling or violent failure.
In the case of metal parts, because of their ductile nature, these systems encourage failure by matting, which can be equivalent to a localized buckling or deformation. In the event of a crash, this mode of failure in the direction of the force is also more dissipative than generalized buckling or violent failure of the part.
In the event of a crash, the failure is initiated locally by a so-called trigger element, e.g. a local variation in thickness, a local cut-out, an impact, etc., which makes it possible to control the failure initiation site and the specified level of force. This function seems to be relatively well mastered at the present time.
However, the structural part's degradation once failure has been initiated still requires improved control, so as to maximize the total amount of energy dissipated. This requirement to control the degradation is all the more important for structural parts with open sections and flat surfaces, which are less stable and therefore even more vulnerable than tubes or boxes to buckling or violent failure.
In order to overcome this problem, solutions proposed by the prior art consist of assembling onto the structural parts additional systems with the function of dissipating energy by the occurrence of a controlled failure in these systems. However, such systems present the drawbacks of having a design and mechanical loading modes that are complex, as well as an energy-dissipation capacity that is inherently limited by their dimensions.